Apparatus for controlling hydraulic surge



Dec. 25, 1956 R. E. SNYDER 2,775,255

APPARATUS FOR CONTROLLING HYDRAULIC SURGE Filed July 19, 1952 2 SheetsASheet 1 INVENTOR.

ROBERT E. SNYDER BYJ nrrosmsvs.

Dec. 25, 1956 R. E. SNYDER APPARATUS FOR CONTROLLING HYDRAULIC SURGE Filed July 19, 1952 2 Sheets-Sheet 2 T IN VEN TOR. ROBERT E. SNYDE' R HTTORNEVS.

United States Patent APPARATUS FOR CONTROLLING HYDRAULIC SURGE Robert E. Snyder, Pasadena, Calif.

Application July 19, 1952, Serial No. 299,896

. 13 Claims. (Cl. 13787) My invention relates generally to the absorption of surge and shock in hydraulic systems, and more particularly to means for by-passing a portion of the line fluid to greatly increase the capacity of the surge absorption unit.

In the general application of hydropneumatic vessels to absorb hydraulic surge in a system or a pipeline, the fixed volume of the unit limits the maximum volume of liquid which the unit may absorb. It is therefore a major object of this invention to provide a relief-type surge control apparatus which will absorb a quantity of surge liquid which is in excess of the normal fixed volume of the unit.

Another object of the present invention is to provide a surge absorption unit in which separatory means between a gas chamber and the line fluid may at some predetermined position open a by-pass so that the line fluid may flow into the gas chamber on the rising portion of the pressure cycle, and then close said by-pass on the falling portion of the pressure cycle.

Hydropneumatic vessels usually consist of a chamber which provides a space for gas against which a surge of liquid may press. In systems wherein it is desired to holdthe pressure within relatively narrow limits, it is obvious that the quantity of surge liquid which a given chamber can receive while maintaining the pressure within the prescribed limits is limited by the available cubic volume of the chamber. However, if as the surge liquid .enters the unit, the unit can by-pass a'certain portion of the incoming liquid, then the rate at which the pressure rises will be diminished and the ultimate pressure held to a predetermined value, back-pressing against the line surge as the liquid flows into, through, and out of the unit during the time period of the surge. Thus another object of the present invention is to provide a controlled by-pass of liquid from the surge absorption unit during the time the surge liquid is flowing into the unit.

In a similar but alternate manner, if the surge chamber can begin to relieve itself of gas pressure after that pressure under compression of the surge liquid reaches a predetermined value, the chamber can continue to receive surge fluid without an undue pressure rise. There fol lows then another object of the invention to provide means whereby the upper gas pressure limit of the chamber can be controlled to that required to stop the liquid surge in the system while the unit continues to accept surge liquid.

In some special hydraulic systems in use today enormous flows of hydraulic fluid are required in the lines, and these flows are subject to shut-01f in periods of time of but a few seconds. Since the dynamic energy of the mass of moving fluid is very great if it is not absorbed and dissipated over a substantial period of time, it will destroy the system designed to contain it. The resultant surge volume of fluid to be absorbed by the hydropneumatic unit thus may be very great, so great in fact that a single chamber necessary to absorb it would beun- 1 economically large. It is therefore an object of the inice vention to provide a hydropneumatic absorber which can absorb very great quantities of surge fluid and yet still be economical in size.

It is a still further object to provide a surge absorption system which will automatically empty out the entrained fluid and then reset and recharge itself after the absorption of one surge, to be in readiness: to absorb another surge of fluid very shortly thereafter.

It has been found that the mere combination of a common relief valve with a hydropneumatic unit is not satisfactory under many conditions. The reseat pressures of standard relief valves usually are at least ten percent of the line working pressure below the pop-o pressure; and further, for sudden shocks and surges, the inertia factor of the relief valve or alleviator is too great to permit the valve to open in time to accept the surge and limit what might otherwise be a dangerous surge pressure rise. Consequently, it is another object of this invention to provide a hydropneumatic unit which will react to sudden surges with extreme speed, and which will reseat again before the line pressure shall have fallen below the average working pressure.

During operation of hydraulic systems there are small but continual pressure variations in the system. A relief valve will not react fast enough to allow the surges causing high pressure peaks to escape, and it can do nothing to mitigate line pressure drops. A hydropneumatic unit, on the other hand, will both accept pressure fluid to avoid sharp pressure rises in the system, and on line pressure drops it will force fluid out into the line to maintain a very close pressure range. Thus a close relationship between the pre-charge pressure of the surge chamber gas and the pressure at which the relief valve will both open and reseat are necessary for smooth operation. A further object of the invention lies in the provision of an inter-control between the pre-charge gas pressure of the hydropneumatic chamber and the pres sure setting of the relief valve operating in conjunction with the surge chamber. t

In order to have a low inertia factor in the surge control apparatus, the separatory means between the gas and theliquid should be as light in weight as possible. In the preferred structure of the present invention a piston-type separatory means is used during a part of the operation of the surge chamber; and then, for absorption of large volumes of fluid the piston is by-passed and no separatory means is used. Thus another object of the invention is the provision of a separatory means between the gas and the liquid during small variations in line pressures, but which separatory means may be bypassed when line pressure rises past a predetermined value to offer minimum inertia resistance to the acceptance of surge fluid by the absorber.

It is a further object of the invention to provide a resetting of the separatory means between the gas and the liquid in the surge chamber after the surge subsides to avoid the entry of the chambers gas into the liquid portion of the system.

These and other objects and advantages of the present invention will become apparent from the specification and the attached drawings, wherein:

Fig. 1 shows a vertical cross section of the hydropneumatic chamber and a schematic layout of the associated controls;

Fig. 2 is an exterior view of the chamber with a portion cut away to show one extreme position of the piston in the chamber;

Fig. 3 is a cut-away section of the piston approaching the port section of the cylinder;

Fig. 4 is a similar cut-away section of the piston positioned across the port section of the cylinder; and

. mulator.

Fig. 5 is an exterior view of an alternate form of the hydropneumatic chamber.

By reference to Fig. 1 of the drawings, the general layout of the surge control system may be seen. It is comprised of a hydropneumatic accumulator which is connected into the main hydraulic system (not shown) through its base member 11. A liquid relief valve 12 is connected to the accumulator 10 to remove fluid therefrom into a reservoir (not shown). The accumulator 10 is further provided with a high pressure gas blow-off relief valve 13 to allow gas compressed above a predetermined pressure to escape. An automatic gas pro-charge system 14 is also connected to the accumulator to maintain the accumulator gas pressure at a predetermined minimum. The liquid relief valve 12 is of the gas cushion type and the critical pressure at which it will pass fluid is controlled by the accumulator pre-chargc system '14.

More specifically, and by reference to Fig. 1, the hydropneumatie accumulator 10 illustrated herein is a piston-type unit wherein the movable piston serves as a separatory member between the accumulator gas and the line liquid. However, the piston has other specific duties in the accumulator, as will be described. The accumulator 10 is comprised essentially of a tubular body which is closed at its upper end by a dished head 21 attached, as by welding, to the tubular body 24). Centrally located on the head 21 is a threaded port 22 through which gas may be put into or removed from the accu- The bottom of tubular body 20 is provided with an annular ring 23 attached, as by welding, thereto. This ring is provided with a plurality of stud bolts 24 threaded and sealed into the ring to form a flange having a circle of stud bolts projecting downwardly therefrom. The lower face 25 of the flange ring is flat and normal to the axis of the accumulator- Concentric with the tubular body 20, a bore 26 extends through the ring 23.

In the side of the tubular body 20, and just above the inner face 28 of ring 23, a threaded drain port 27 is afiixed. The size of this port in the present drawings is relatively small. However, this is by way of illustration only, and for field operation its size is established by the required rate of flow of liquid therethrough as determined by the required operating characteristics of the system.

Located centrally within the tubular body 20 is a tubular member 30 having its bore 31 honed and polished to form a smooth straight cylinder. To the lower end 32 of the inner tubular member 30, a flange 33 is affixed as by welding. The upper and lower faces 34 and 35, respectively, of flange 33 are both flat, smooth, and normal to the axis of the tubular member 30. The flange 33 further contains a series of holes 36 complementally placed to the studs 24 in ring 23. When the tubular member 30 is passed through the bore 26 into the interior of the outer tubular body 20, a boss 37 machined on the upper face of the flange 33 maintains concentricity between flange 33 and the ring 23. The stud bolts 24 pass through the holes 26 in flange 33 and the upper face 34 of flange 33 and the lower face 25 of ring 23 may be sealably engaged across a seal ring 38 positioned between the faces.

The upper end 40 of cylindrical member 30 is provided with a coupling 41 attached axially concentric thereto. A plug 42 is threadedly engaged within coupling 41, and in the center of the plug a port 43 insures free flow of gas into and out of the upper portion of the cylindrical member 30. To the underside 44 of plug 42, 'a buffer spring 45 is afl'ixed by bracket 46, which is screwed to the plug by a plurality of screws 47. The free end 48 of spring 45 hangs concentrically down inside the cylindrical member 30.

Riding in bore 31 of cylindrical member 30 is a piston 50 having a solid face '51 and a plurality of packers 52 and guide rings 53 adapted to provide a sliding seal of the piston within the bore 31 and dividing the interior of cylinder 30 into two dependently variable chambers 55, above the piston, and 56, below the piston.

As piston 50 moves upwardly in bore 30 decreasing the volume of gas chamber 55, face 51 of the piston engages the lower end 48 of spring 45. Further upward movement of piston 50 finally compresses spring 45 to its solid stack height, as may be best seen in Fig. 2. The gas in the now minimum-sized chamber 55 may escape through port 43.

The base 11 of the accumulator 10 is preferably comprised of a special T-shaped steel casting having a central body portion from which extend three portions 61, 62, and 63 carrying the flanges 64, and 66, respectively. The flanges 64 and 65 may be standard pipe flanges of any of several well-known types as might be required by the line pipe adapted to be joined thereto. The direction of flow of liquid through the unit is indicated by the arrows wherein the line fluid enters from the line (not shown) through the flanges 64 and passes into bore 67 and into a bore 68 which intersects bore 67 at right angles. The liquid passes then through bore 68 and out through flange 65 into the line (not shown). The bore 67 further extends upwardly through the base 11, upper flange 66, and into the fluid chamber 55 of the accumulator. The flange 66 is provided wtih a flat, smooth upper face 69 normal to the axis of bore 67, and having a plurality of holes 70 arranged eomplementally to the stud bolts 24 in ring 23.

The flange 66 is advanced toward studs 24 so that the holes 70 fit around the studs, and the upper face 69 is advanced toward the lower face 35 on the bottom of the flange 33. A packer 75. is positioned between the two faces 69 and 35 to seal the interstice. A boss 76 extend ing above the upper face 69 from base 11 enters into the bore 31 of cylindrical member 30 to further maintain the axial concentricity of'the base 11 with the bore 31 of the cylindrical member 30. A nut 77 is then placed upon each of the studs 24 and tightened against the flange 66, thereby tightening all three flanges 66, 33, and 23, respectively, toward each other, sealing all joints against the respective packers 38 and 75. The tightened stud bolts also hold all three elements, the outer tubular body 20, inner cylindrical member 30, and the base 11 into a rigid structure comprising the complete accumulator 10.

The bore 67 passes through base 11 and boss 76 into the chamber 56. The upper face 80 of boss 76 forms the bottom of chamber 56 and also serves as a stop for piston 50 in its extreme downward position in the bore of cylindrical member 30. In this extreme downward position of the piston 50, the liquid chamber 56 is at its minimum size and the gas chamber 55 is at its maximum size.

The interior of the accumulator 10 is thus divided into several chambers. The outer chamber encompasses the annular space defined by the outer tubular body 20, dished head 21, lower flange ring 23 and the outside of inner tubular member 30. Within the tubular member 30 the movable piston 50 divides the space into two dependently variable chambers, 55 above the piston and 56 below the piston. The upper chamber 55 is connected to the outer chamber 90 by port 43 in the upper end of the tubular member 30. The lower chamber 56 is open to the line fluid through the bore 67 in base 11. The outer chamber 90 is further connected to the lower drain port 27 just above flange ring 23 and also to the gas port 22 in dished head 21.

Another set of portsv is positioned in the walls of the tubular member 30 connecting the interior of member 30 with the annular outer chamber 90. These ports 95 connect the outer chamber 90 to upper chamber 55 when piston 50 is below them in the tubular member 30, and they also connect the outer chamber 90 to lower chamber 56 when piston 50 has moved across and above them in the tubular member 30. The piston 50 is adapted thus to travel back and forth across the side ports 95 in a manner and for reasons hereinafter to be described.

The side ports 95 are positioned near the upper end of tubular member 30 and at a distance below the coupling 41 determined by the relationship of the spring 45 and piston 50. In general, the dimensional relationships are illustrated in the structures shown in Figs. 1 and 2 wherein the spring 45 contacts the solid portion 51 of piston 50 just as the piston starts to cross the ports 95 but before at least the lower piston packer 52 has started to cross ports 95. Further upward motion of the piston 50 allows the lower packer 52 of piston 50 to move above the lower portion of ports 95 and open them to connect the outer chamber 90 to the inner chamber 56. The extreme upward position of piston 50 against the fully compressed spring 45 Within tubular member 30 can best be seen in Fig. 2.

When the pressure of the line fluid forces piston 50 above the side ports 95, the line fluid can then flow through these ports directly into the outer chamber 90 as long as the line pressure can hold piston 50 above these side ports 95. However, when the line pressure falls below the gas pressure in the gas chamber 55, the combination of spring pressure and gas pressure upon the upper face 51 of piston 51 will force the piston downwardly to close 011 the ports 95 and shut 011 the flow of fluid from chamber 56 into outer chamber 90 of the accumulator. The action of spring 45 insures the piston 50 closing the ports 95 without the loss of gas through ports 95.

By reference to Figs. 3 and 4 the action of piston 50 with its packers 52 and guide rings 53 as it crosses the ports 95 can be seen. Immediately adjacent the lower end of ports 95, the bore 31 is enlarged. to provide a smooth tapered portion 100 to an enlargement of the bore over the area 101. This enlarged bore extends upwardly across ports 95 to a point above the ports where a second tapered portion 102 reduces the enlarged bore 101 back to the original diameter of the bore 31. This enlarged bore area 1131 is sufiicient to remove all squeeze from packers 52 so that they will not roll over and be cut on the edges of the ports 95. The cylindrical wall segments 103 between the ports 95 serve to guide the piston past the ports 95. The split guide rings 53 expand slightly in moving from the bore 31 into the enlarged portion 101 of the bore to thereby hold piston 50 substantially concentric within the bore and hold the piston from cooking and jamming in the bore during its upward or downward movement past the ports 95.

Fig. 3 shows the piston 50 as it starts to cross the ports 95 on its upward stroke, or as it leaves the area of the ports 95 on its downward movement. Fig. 4 shows the position of piston 59 in the midway position across the ports 95.

Turning now to the automatic gas pre-charge system 14 shown in Fig. 1 of the drawings, it is seen toinclude a source 126 of neutral gas such as, for example, a bottle of nitrogen. A standard pressure reducer 121 including the necessary gauges 122 and 123 is used with the gas source to enable the operator to establish and hold the pressure for the accumulator pro-charge gas to a predetermined and constant value. Such sources and regulators are well known to the art and their capacity and design will be subject to the other operational prerequisites of the surge control system. From the regulator the gas passes through a pipe 124, through a line check valve 125 and into the main gas pre-charge valve 126.

The structure and operation of the gas precharge valve 126 has been described in my presently copending patent application Serial No. 400,687, and so it will not be completely described in this specification. However, for the purposes of the control system in this present invention the valves operation may be briefly described as follows. From a port 130 in the accumulator base 11 met any other convenient point in the main line where a characteristic main line pressure may exist, a pipe 131 is carried up into the gas pre-charge valve 126 through a port 132.

Within the gas pre-charge valve the main line pressure is brought to bear against an appropriate diaphragm means in order to operate the gas pre-charge valve in a manner that when the line pressure is less than the gas pro-charge pressure, as set by regulator 121, the gas pre-charge valve will pass pre-charge gas into line 133. However, when the line pressure rises above the pressure established by the regulator 121, the gas pre-charge valve Will shut otf and permit no gas to pass from pipe into line 133.

From the line 133 the gas from valve 126 passes into the T 134 from which it may pass into the lines 135 and 136. In the line 135 it passes upwardly through a check valve 137 into a line 138 and on into T 139. From T 139 the gas passes into lines 140 and 141. In line 140 the gas passes through a manual shut-011 valve 142 into a line 143 and a T 144. From one port of T 144 connected directly to the gas port 22 of accumulator 10, the gas may pass into the chamber 90 of accumulator 10, the gas may pass into the chamber 90 of accumulator 10 and from there through ports 95 and 43 into the upper chamber 55. The other port of T 144 connects to a line 145 and to a manual blow-off valve 146. By shutting off the valve 142 and opening valve 146 all the gas pressure within accumulator 10 can be blown off to the outside air. By closing valve 146 and opening valve 142 the accumulator 10 can be pre-charged with gas from the source 120 at the pressure preset by regulator 121 as long as such pro-charge pressure is greater than the pressure in the main line. i

The line 141 from T 139 terminates in the main gas relief valve 13. This relief valve 13 is of standard make and by the adjustment of the pressure exerted against its poppet valve 150 by spring 151 under the control of the hand adjustment screw 152 any required pressure may be established at which the relief valve 13 will by-pass gas from the chamber 90 of accumulator 10 to the outside air.

The liquid relief valve 12 which operates in conjunction with accumulator 10 may be of any preferable size to remove whatever desired quantity of liquid per unit time the operation of the particular surge control installation may require. The size of the liquid relief valve shown in Fig. l is by way of illustration only.

The valve consists essentially of a body having a fluid inlet port 161 and a fluid outlet port 162, the inlet port 161 being connected by a pipe 163 to the drain port 27 of accumulator 10, and the outlet port 162 being connected to a pipe 164 leading to a reservoir (not shown) or to any other convenient disposal place for the liquid output from the relief valve 12. Within the body 160 of relief valve 12 a cross member 165 divides the interior space into two chambers 166 and 167, the first chamber 166 being open to inlet port 161 and the second chamber 167 being open to outlet port 162. An opening 168 in the cross member 165 provides a seat for a poppet-type valve 169 which rides on a stern 170 between guides 171 in the base of body 160, and 172 in the upper portion 173 of the valve body. A light compression spring 174 surrounding the stem 170 and pressing upwardly against the upper portion 173 and downwardly upon the valve 169 insures the valve being normally closed.

Within the upper portion 173 a metal Sylphon diaphragm 175 is positioned, the closed lower end of which is attached to the upper end of valve stem 170 and the upper end of which is sealed between a flange 176 on the upper portion 173 and a second flange 177 on the bottom of the hydropneumatic gas ballast chamber of relief valve 12. A port 178 connects chamber 167 with the annular space between the inside of upper portion 173 and the outside of Sylphon 175.

The gas ballast chamber 180 consists of a tubular body 181 having a flange on its upper end, and an opening 182 in the bottom covered with a multi-orificed plate 183. Within body 181 a flexible diaphragm 184 of synthetic rubber or her uit le m rial uc a metal ic Sylphon, divides the chamber into two interdependent, chambers186 above the diaphragm, and 187 below the diaphragm. A liquid channel 190 extends from the inside of diaphragm 175 through a pipe 191 to a check valve 192 and an orifice valve 193, which are in turn connected in parallel to a pipe 194. From the pipe 194 liquid may travel through liquid channel 195 and orifice plate 183 into chamber 187. The chamber 187, the pipes 194 and 191, the two liquid channels 190 and 195 as well as the inside of Sylphon 175 are filled with a liquid 196.

, The top of the gas ballast chamber is closed with a flange 200 and contains a gas port 201 therein through which gas may be put into the upper chamber 186. It is thus evident that the gas pressure within the chamber 186 against the diaphragm 184 will be transferred to the liquid 196 and from thence through the Sylphon diaphragm 175 to the valve stem and down to the valve 169..

The gas ballast chamber is connected through gas port 201, a pipe 202, a manual shut-off valve 203, a pipe 204, and a check valve 205 to the pro-charge gas available in the pipe 136. By shutting oif the manual valve 203 and by opening hand shut-off valve 206 connected to pipe 202, all the gas pressure in the gas ballast chamber can be blown off to the air. Or, by closing the valve 206 and opening valve 203, the gas ballast chamber can be brought up to the same pre-charge gas pressure as that in the chamber 91) of accumulator It). By proper regulation of the gas pressure in the gas ballast chamber 180 in view of the effective area of the Sylphon 175 and the seat area of the poppet valve 169, a direct relationship between the gas pressure and the line pressure at which the relief valve 12 will allow liquid to pass from chamber 166 to chamber 167 will be established. Thus the relief cracking pressure of relief valve 12 can be made equal to the gas pro-charge pressure of the accumulator, or by changing various relationships between the Sylphon 175 and the poppet valve 169, any particular relationship or ratio between the relief valve pop-01f pressure and the accumulator gas pre-charge pressure can be established.

The. surge absorption system shown in Fig. 1 may be operated in diiferent ways, depending upon varying types of surges which it must control. However, in all cases the surge chamber 10 is connected into the hydraulic system or main pipe line by flanges 64, and 65. The liquid in this system flows through the base 11, entering through the flange 64 into chamber 67, then passing into chamber 68 and out into the pipe line through flange 65;

and the line liquid in the chamber 67 enters up into I chamber 56 and against the underside of piston 50.

The adjustment of the rest of the units in the surge absorption system, to wit, the gas pre-charge regulator 12]., gas pre-charge valve 126, liquid relief valve 12, gas relief valve 13, and the manual valves 142, 203, and 206 may be varied for different operating conditions.

One method of operation may be described as follows. The liquid relief valve 12 has a ratio of its valve 169 and Sylphon diaphragm 175 established that it will open when the liquid pressure in chamber 166 is a few pounds above the gas pro-charge pressure in the chamher 186 and will reseat when the liquid pressure in chamber 166 has fallen a few pounds below the gas precharge pressure in the chamber 186. The range of pressure between the opening and the reseating pressures of this relief valve 12 is related to the changes of pressure in the accumulator 10 due to movement of piston 50, as will be further discussed.

The hand valves 142 and 203 are closed and the gas pre-charge regulator 121 is set to a value slightly below the average working line pressure to be found in the line liquid in the chambers 67, 68, and 56 of accumulator 10. During the gas pro-charging of accumulator 10 and relief valve 12, the line liquid pressure is held as close to zero as is practical, atleast substantially below the line; working pressure. The valve 206is, closed tight,

valve 203 is opened, and chamber 186 of the relief valve 12 is pre-charged with gas. When its pressure has reached the pre-charge value, valve 203 may be closed, though this is not absolutely necessary if the check valves 205 and 137 are found to be leak-tight in their check positions.

The main accumulator 10 is pro-charged by closing valve 146 tightly and opening valve 142. The pre-charge gas will enter the annular chamber and chamber 55, pushing the piston 50 to its extreme down position against the lower stop 76 in base 11. After the accumulator 10 has been pro-charged, the hand valve 142 is partially closed down so that the subsequent rate of entry of gas into the accumulator 10 shall be less than the rate of drain of liquid from the chamber 90 of accumulator 10 through relief valve 12. The gas relief valve 13 is adjusted to open at some maximum pressure which is the upper limit deemed advisable for the system.

The main line liquid pressure below piston 50 may now be turned on. This pressure being slightly above the initial gas pre-charge pressure will cause piston 50 to move upwardly against the pre-charge gas, compressing it. The piston will stop its upward movement when the gas pressure in chambers 90 and 55 has become equalized to that of the line liquid pressure below the piston, and the piston will float in the cylinder 30 between the line liquid and the accumulator gas, separating them from contact and intermixture.

As the gas pressure in chamber 90 rises above the preset pre-charge value due to increased pressure of the line liquid, it backs up through T 144, line 143, valve 14-2, line 140, T 139, and the lines 138 and 141 against check valve 137 and gas relief valve 13, respectively. The check 137' seals off and stops its further progress and the gas relief valve holds it against escape as long as it remains below the preset critical blow-off pressure. The line working pressure of the hydraulic liquid, from the boss 130. in base 11 travels through line 131 and the boss 132 into pre-charge valve 126, closing it and shutting off any further flow of gas from line 124 into line 133.

In this condition of the system, small pressure variations of the line fluid in chamber 56 below piston 50 merely cause the piston to oscillate up and down well below the by-pass ports to balance out the variations. However, in the event of a sudden rise in line pressure the piston 50 very rapidly moves upwardly past ports 95 and the line fluid will then by-pass below piston 50 through the ports 95 and into annular chamber 90. The line pressure at which this liquid will first pass through ports 95 is a critical pressure and its relationship to the original gas pro-charge pressure must be known because of its relationship to the subsequent action of liquid relief valve 12. In order that relief valve 12 shall not allow the escape of the pre-charge gas, it is adjusted so that it will not open until after the critical pressure has been reached, i. e. until liquid shall have passed through ports 95 below the piston 50 and down into the bottom of chamber 90. After the line liquid has entered chamber 90, the opening of relief valve 12. will allow this liquid to pass out of the chamber 90.

If, with substantial liquid flowing in the main line through base 11, the flow is suddenly cut ofi at some point along the line outside of flange 65, there will result a surge of fluid from the line through the flange 64 which will travel into accumulator 10. The piston 50 will be pushed to its upper limit against spring 45 and the liquid will by-pass below it into the annular chamber 90. The entry of this fluid into the unit causes the gas pressure to rise, and when it has passed the critical value, the relief valve 12 opens and the liquid starts to drain out of chamber 94) through pipe 163, relief valve 12, and the pipe 164. The rate at which it drains out can be fixed for any particular system by the use of suitably sized pipes and valves.

However, the main gas cushion in the accumulator 10 absorbs the surge fluid smoothly and prevents the format valve 12 opens.

tion of any shock or counter-surge waves in the system, While the surge of fluid is cushioned against a smoothlyrising pressure of gas. This pressure rise may be limited or controlled to any predetermined degree by the combination absorption of the gas cushion and the action of the relief valve to drain off the entrained fluid. in this manner the dynamic energy of the fluid surge may be absorbed and dissipated.

If the relief valve 12 can drain the fluid out substantially as rapidly as it enters chamber 90, the gas pressure will not rise appreciably further after the relief On the other hand, if the surge fluid enters more rapidly than relief valve 12 can drain it out, then the gas pressure will continue to rise, but at a rate determined by the difference of the two flows of fluid. If the gas pressure still rises to the value at which the gas relief valve 13 will open, this will drain high pressure gas from the unit. In this case a constant upper limit of gas pressure will continue its back pressure against the surge while the accumulator continues to accept surge fluid faster than relief valve 12 can drain it from the chamber 92. However, a surge of fluid does not last for a very long period, and the high back pressure of the gas will rapidly slow it down and stop it.

This surge absorption system will thus accept a total Volume of fluid far greater than a correspondingly sized unit not so provided with a liquid or a gas relief system.

When the surge of line fluid slackens oif, the combination of gas pressure in chamber 90 and the pressure of spring upon piston will force the piston back down across the ports 95 and shut off the flow of line liquid into chamber 90. The gas pressure will continue to force the piston 50 downwardly in cylinder 30 until it seats against the stop 76 of base 11, and the gas pressure in chamber 90 will continue to force the liquid remaining in the chamber 90 out through relief valve 12.

If theliquid drain through the relief valve 12 is rapid enough to avoid the gas pressure rising to a point where the gas relief valvewill open, very little gas will be lost in absorbing a single surge, and the gas in the unit will be suflicient to blow out substantially all of the liquid received into the chamber 90 before its pressure shall have fallen to a point where the relief valve 12 will close. But if gas is lost, either through the gas relief valve 12 or through solution into the line fluid passing through the chamber 90, there maybe a net gain of liquid which will remain in chamber 90 from consecutive surges, which will not be removed by relief valve 12 before closing due to the low pressure of the gas remaining in the chamber 99. In such cases, manual adjustment of the relief valve 12 by closing valve 203 and opening valve 206 periodically will reduce the relief pressure and allow all the liquid to be blown out of the chamber 90, after which the closing of valve 206 and the opening of valve 203 may again reset the relief valve to its original value. Under most conditions of service, such manual operations are not necessary and the unit will be entirely automatic.

The system can be operated with a standard spring or counterweight-type relief valve in place of the gas cushion type as shown in relief valve 12 of Fig. 1. However, the adjustment of such valves to a given pre-charge of the accumulator 10 is not so easy. to accomplish.

The accumulator 10, though in a less efficient manner, can also be operated without a fluid relief valve 12 and by the use of the gas relief valve 13 alone during its adsorption of a surge of liquid. In this case, all the liquid from the surgewould be stored within the ac cumulator 10 and this liquid would merely back up against a maximum pre-set gas pressure, as determined by the setting of the gas relief valve 13. At the end of the surge cycle, the entrained liquid would have to be removed from the system by a suitable, valve, prior to its pre-charging and return to use in the line.

In the system as shown in Fig. I, after the surge has subsided and the liquid drained frointhe chamber 90, the main linepressure is reduced to a value substantially below that of the gas pre-charge value and the gas recharging of the unit begins. The reduction of the main line pressure automatically allows the gas precharge valve 126 to open and gas flows from regulator 121 through precharge valve 126 into pipe 133, from which it flows through the attached piping into chamber 186 of relief valve 12 and into the chamber of accumulator 10 at a relatively slow rate through the orificed hand valve 142. The correct orificing of valve 142 should allow the liquid relief valve 12 to drain substantially all of the entrained fluid from chamber 90 and the gas pressure to drop below that necessary for the relief valve 12 to resent itself before the gas pressure in the chamber 90 builds up again to the normal pro-charge value. If the pre-charge is built up too rapidly, the relief valve 12 will not close, but will remain open and drain pre-charge gas from the chamber 90.

The system of pre-charge and the liquid relief valve controls shown in Fig. l of. the drawings and the above method of operation are but one of many possible types of controls and methods of control which can be applied to the relief-type accumulator 10 shown herein. The present system is in general merely illustrative of how the accumulator 10 can be used in such a system.

By reference to the accumulator structure in Fig. 5 an alternate form of the relief-type piston bypass valve is shown. In this assembly, in contrast to the structure shown in Fig. 1 where the piston 51) moves across the ports within the cylinder 30, the piston 210 has a valve 211 built into it which, when the piston reaches the upper limit of its movement, is opened to by-pass the line liquid through the piston 210. in the Fig. 5 structure, parts identical to those in Figs. 1 and 2 have similar numbers with an added a. The outer shell of the accumulator 10a is identical to that of Fig. 1, except that the inner tubular member 30a is threadedly joined to a boss 76a on the upper end of base 11a. The flange ring 23a is directly joined to the base flange 66a by studs 24a and nuts 77a. The upper end of tubular member 30a is provided with awebbed stop member 212 which contains a solid central stop portion 213 joined to the rim 214 by a plurality of webs 215. The rim 214 of stop member 212 is aflixed to the upper end of tubular member 30a as by welding. The space 216 between the webs 215 provides a port opening between the inside of the tubular member 30a and the annular chamber 90a of accumulator 10a.

The piston 210 slides inside the tubular member 30a between the upper stop member 212 and the lower stop face 217 on the upper end of the boss 76a on base 11a. The piston 210 is comprised of a central body portion 220 having a plurality of packers 52a and a pair of guide rings 53a mounted on the outside thereof. Mounted centrally in the piston 210 is a bearing 221 supported by webs 222 integral with the piston body 220 which webs provide a fluid passage through the piston 210. Journaled within bearing 221 is a valve stem 225 provided at its lower end with a flanged head 226 and at its upper end with a shouldered stop 227. Between the underside of shouldered stop 227 and the upper side of webs 222, and around the outside of bearing 221 is a compression spring 230. p

The lower end 235 of piston 210 is provided with a tapered seat 232 complemental to the flanged head 226 and within which the flanged head is adapted to make a fluid and gas tight seal. The compression spring 230 urges the flanged head into a tight sealing position against the valve seat 232. When the valve piston assembly is in the lowermost position within the tubular member 30a, the lower face 233. of flanged head 226 rests against the stop face 217 on boss 76a, as may be seen in the dotted outline of the piston in Fig. 5.

When. piston. 210 approaches the upper limit of its travel within tubular member a, the shouldered stop 227 on the upper end of valve stem 225.contacts the solid central stop portion 213 of the webbed stop member 212 in the upper end of tubular member 30a. Further pressure of the line fluid against the lower annular face 235 of piston 210 further raises the piston against the pressure of spring 230 and the gas pressure above the piston, opening flanged head 226 and allowing the line fluid to pass through the webbed portion of piston 210, and the webbed portion of webbed stop member 212 into chamber 90a. A decrease in the line fluid pressure permits spring 230 to push the piston body 229 downwardly permits, spring 230 to push the piston body 220 downwardly and close flanged head 226 against the seat 232. Further decrease of the line fluid pressure enables the gas in chamber 90a to push the whole valve-piston assembly downwardly within the tubular member 30a.

In operation in a hydraulic system in the absorption of hydraulic surge, this structure operates in substantially the same manner as that previously described for the accumulator shown in Figs. 1 and 2. Its utilization of the other automatic pre-charge and fluid release elements of the control system outlined in Fig. l is likewise similar. While I have described my invention with relation to particular forms of my surge absorption device, it will be apparent that modifications can be made in each of the forms, and in combinations of features other than those set forth. Accordingly, I do not wish to be restricted to the details of construction herein described, except as. defined in theappended claims.

I claim:

1. A relief-type hydropneumatic surge absorber comprising: a' gas-tight vessel; a gas port in said vessel opening into the interior thereof, through which port said vesselmay be pro-charged with gas at a predetermined pressure; a cylindrical member having one end connected to said vessel; a by-pass port from said cylindrical memher to the interior of said vessel; a liquid port opening into the other end of said cylindrical member; means connecting said liquid port to a liquid line, whereby the line liquid may enter said cylindrical member; a piston. slidably mounted within said cylinder, the side of said piston toward said liquid port contacting the line liquid, and the other side of said piston contacting the precharge gas, said piston being adapted to open and to close said by-pass portv to the entry of the line liquid into the interior of said vessel against the pro-charge gas at a predetermined position of the stroke of said piston within said cylinder; and a gas relief valve connected to said gas port whereby gas may escape from said vessel when the entry of liquid thereinto through said by-pass port shall have raised the gas pressure to a predetermined value and means for draining liquid from said vessel.

2. A relief-type hydropneumatic surge absorber comprising a gas-tight vessel, comprising: an outer shell; a gas port in said shell opening into the interior thereof; a flange having an opening therein on the lower end. of said shell; a tubular member extending through the opening in said shell flange into the interior of said outer shell; a flange on the lower end of said tubular member having an upper face complemental to the outer face of said shell flange, said two flanges being adapted to seat against each other with a sealing gasket" therebetween; a base member; a flange on the upper end of said base member having an upper face complemental to the lower face of said tubular member flange, said two flanges being adapted to seat against each other with a sealing gasket therebetween; fastening means adapted to engage said. shell flange and'said base flange to draw said two flanges toward each other and sealing said tubular member flange with. saidv two gaskets into a tight joint; a' port in'said base adapted to be connected to a liquid line; a second port in said base connected to said first port and opening into the interior of said tubular member, whereby the line liquid may enter said tubular member; a by-pass port in said tubular member opening from the interior of said tubular member into the interior of said outer shell; a resilient stop within said tubular member adjacent said by-pass port; a second stop within said tubular member on said base adjacent said second port in said base; and a piston mounted within said tubular member between said by-pass port and said second port in said base, and slidable within said tubular member between said two stops, said piston being adapted to open and to close said by-pass port to access to said second port in said base at predetermined positions of its stroke within said tubular member between said two stops and means. for draining liquid from said vessel.

A relief-type hydropneumatic surge absorber comprising a gas-tight vessel, comprising: an outer shell; a gas port in said shell opening into the interior thereof; a flange having an opening therethrough on the lower end of said shell; a base member; an open ended tubular member upon said base member and extending therefrom through the opening in said shell flange into the interior of said outer shell; a flange on the upper end of said base member surrounding said tubular member and having an upper face complemental to the lower face of said shell flange, said two flanges being adapted to seat against each other with a sealing gasket therebetween; fastening means adapted to engage said shell flange and said base flange to draw said two flanges toward each other and against the sealing gasket into a tight joint; a port in said baseadapted to be connected to a liquid line; a second port in said base connected to said first port and opening into the interior of said tubular member, whereby the line liquid may enter said tubular member; a by-pass port in said tubular member opening from the interior of said tubular member into the interior of said outer shell; a stop within said tubular member adjacent said by-pass port; a second stop within said tubular member on said base adjacent said second port in said base; a piston mounted within said tubular member between said by-pass port and said second port in said base, said slidable within said tubular member between said two stops, and comprising a tubular body; packing means between said body and said tubular member; a valve guide mounted within said body; a valve mounted in said guide, the stem of said valve being adapted to contact said flrststop in said tubular member;

a valve seat upon the lower face of said body against which said valve makes sealing engagement; and a spring between said valve and said body adapted to hold said valve normally closed against said body, said piston being adapted to open said valve, when said valve stem contacts said first stop, and said spring to close said valve when said piston moves said valve stem out of contact with said first stop, to liquid flow from said second port in said base to said by-pass port at predetermined positions of said piston within said tubular member and means for draining liquid from said vessel.

4. A relief-type hydropneumatic surge absorber comprising: a gas-tight vessel; a gas port in said vessel opening into the interior thereof; a cylindrical member fluid connected to said vessel; a liquid port opening into one end of said cylindrical member; a piston slidably mounted within said cylinder, liquid from said liquid port contacting one side of said piston, and gas from said gas port contacting the other side of said piston; means in said cylinder limiting the movement of said piston in said cylinder; a port-in said piston connecting the two sides of said piston; a valve in said piston port; means urging said valve into a normally closed position; and means opening said valve in said piston when said piston is urged by fluid from said fluid port against a stop on the gas end of said cylinder and means for draining liquid from said vessel.

5. In'combination with a hydraulic line, apparatus for absorbing surge in the line including a hydropneumatic accumulator having a liquid chamber connectable with the line to respond to pressure in the line, said chamber having a wall movable in response to pressure change thereon; means cushioning the surge in the line including a fluid-tight gas chamber, the movable wall being a part of the walls defining said gas chamber, said chambers having a passage for the flow of liquid from the liquid chamber to the gas chamber, said movable wall having a section forming a valve normally preventing the flow of liquid through said passage, and said movable wall being operable when moved to a predetermined position to cause said valve to open the passage.

6. A device as defined in claim in which the gas chamber is provided with a liquid drain together with a relief valve connected with and responsive to a change in a fluid condition in the gas chamber for controlling the flow of liquid through the drain.

7. A device as defined in claim 5 in which the gas chamber is provided with a liquid drain together with a relief valve connected with and responsive to the pressure in the gas chamber for controlling the flow of liquid through the drain.

8. A relief-type hydropneumatic surge absorber comprising: a closed gas-tight vessel providing a surge cushioning gas chamber having a gas port opening into the interior thereof through which port said vessel may be pre-charged with gas to a predetermined pressure and a valve liquid drain port opening into the interior of said vessel for periodically draining liquid from said vessel; means associated with said gas port to retain the precharge of gas in said vessel; an elongated cylindrical member having a liquid by-pass port adjacent one end of said cylindrical member communicating with said vessel; means connecting the other end of said cylindrical member to a liquid line whereby liquid may enter said cylindrical member; and a piston slidably mounted within said cylindrical member, the side of said piston toward said connecting means contacting the line liquid and forming a liquid chamber in said cylindrical member and the other side of said piston contacting the pre-charge gas, said piston being movable in response to pressure surges in said liquid line to open and to close said by-pass port to the entry of the line liquid into the interior of said vessel at a predetermined position of said piston within said cylindrical member.

9. A relief-type hydropneumatic surge absorber comprising: a closed gas-tight vessel providing a surge cushioning gas chamber having a gas port opening into the interior thereof through which port said vessel may be precharged with gas to a predtermined pressure and a valved liquid drain port opening into the interior of said vessel for periodically draining liquid from said vessel; means associated with said gas port to retain the pre-charge of gas in said vessel; an elongated cylindrical member within said vessel having a liquid by-pass port adjacent one end of said cylindrical member communicating with said vessel; means connecting the other end of said cylindrical member to a liquid line whereby liquid may enter said cylindrical member; a piston slidably mounted within said cylindrical member between said connecting means and said by-pass port forming a movable separatory wall therebetween, the side of said piston toward said connecting means contacting the line liquid and the side of said piston toward said by-pass port contacting the prechange gas, said piston being movable to open and to close said by-pass port to the entry of the line liquid into 14 the interior of said vessel against the pressure of we charge gas at a predetermined position of said piston within said cylindrical member; and resilient means cooperating With said piston and said cylindrical member to aid in closing said by-pass port against the entry of line liquid.

10. Apparatus for absorbing pressure surge in a hydraulic line including a hydropneumatic accumulator having a liquid chamber and a fluid-tight gas chamber; means for connecting said liquid chamber with the hydraulic line; said gas chamber having a valve controlled liquid drain for periodically draining liquid from said gas chamber and a gas port to enable pre-charging said gas chamber with gas to a predetermined pressure; means associated with said gas port to retain the pro-charge of gas in said gas chamber; said chambers having passage means for the flow of liquid from the liquid chamber to the gas chamber; and means for controlling the flow of "liquid through said passage means including a movable wall member exposed on its opposite sides to the pressures existent within said gas chamber and said liquid chamber respectively, said movable wall member being responsive to surge pressure in the liquid chamber to eifect control of the flow of liquid from said liquid chamber into said gas chamber through said passage means.

11. Apparatus as recited in claim 10 wherein the valve controlling said liquid drain comprises a normally closed relief valve connected with and responsive to a change in a fluid condition in the gas chamber to control flow of liquid through the drain.

12. Apparatus as recited in claim 10 together with an automatic gas pre-charge system comprising a source of gas under pressure connected with the gas chamber; a regulating valve for controlling the flow of gas from the source to the gas chamber; and means responsive to pressure in the hydraulic line for controlling the regulating valve in response to the pressure difierential between said gas chamber and said liquid line.

13. Apparatus as recited in claim 10 wherein the valve controlling said liquid drain comprises a normally closed relief valve connected with and responsive to pressure in the gas chamber to control flow of fluid through said drain; and an automatic gas pro-charge system is provided comprising a source of gas under pressure connected with the gas chamber; a regulating valve for controlling the flow of gas from said source to the gas chamber, and means responsive to pressure in the hydraulic line for controlling the regulating valve in response to the pressure diflerential between said gas chamber and said liquid line.

References Cited in the file of this patent UNITED STATES PATENTS 417,329 Marsh Dec. 17, 1889 860,820 Norton July 23, 1907 1,846,577 Barber Feb. 23, 1932 1,848,531 Lamb Mar. 8, 1932 2,138,654 Doran Nov. 29, 1938 2,261,364 Grove Nov. 4, 1941 2,417,873 Hyber Mar. 25, 1947 2,583,215 Helm Jan. 22, 1952 FOREIGN PATENTS 516,944 France Dec. 10, 1920 328,654 Great Britain May 1, 1930 561,694 Germany Oct. 17, 1932 

